1. Field of the Invention
The present invention relates to an induction motor, and particularly, to an induction motor controller.
2. Description of the Conventional Art
FIG. 1 is a view schematically showing a construction of an induction motor in accordance with the conventional art.
As shown in FIG. 1, the induction motor in accordance with the conventional art largely includes: a stator 100; an induction rotor 120; a permanent magnet rotor 140; and a rotating shaft 110.
The stator 100 is made up of main coils 160A and 160B and sub-coils 160C and 160D respectively wound around an iron core 150 of the induction motor. Here, the main coils 160A and 160B and the sub-coils 160C and 160D are sequentially connected in series such that the coils adjacent to each other have the same polarities.
The permanent magnet rotor 140 consists of a ring type permanent magnet (not shown) installed between the stator 100 and the induction rotor 120 at a predetermined gap and a permanent magnet supporting unit (not shown) for supporting the ring type permanent magnet. Also, to make the permanent magnet rotor 140 rotated centering around the rotating shaft 110, a bearing 130 is installed between the permanent magnet supporting unit and the rotating shaft 110.
Hereinafter, a circuit of the induction motor in accordance with the conventional art Will be described with reference to FIG. 2.
FIG. 2 shows a circuit of an induction motor in accordance with the conventional art.
As shown in FIG. 2, the circuit of the induction motor in accordance with the conventional art includes: the main coils 160A and 160B and the sub-coils 160C and 160D connected in parallel with power terminals (A and B); and a capacitor 200 electrically connected between a terminal (MAIN) of the main coils 160A and 160B and a terminal (SUB) of the sub-coils 160C and 160D.
A common terminal (COM) to which the main coils 160A and 160B and the sub-coils 160C and 160D are connected is electrically connected to the power terminal (A), and the terminal (MAIN) of the main coils 160A and 160B is electrically connected to the power terminal (B). In addition, in order to operate the induction motor with high efficiency, the winding number of the main coils 160A and 160B and the sub-coils 160C and 160D of the induction motor is designed so as to be suitable for high efficiency features. Namely, in order to operate the induction motor with high efficiency, the winding number of the main coils 160A and 160B and the sub-coils 160C and 160D is determined according to the power (AC).
Hereinafter, an operation of the induction motor in accordance with the conventional art will be described.
First, if the power (AC) is supplied to the power terminals (A and B), the power (AC) is applied to the main coils 160A and 160B, and simultaneously to the sub-coils 160C and 160D through the capacitor 200.
Thereafter, a leading current with a 90 degree phase difference flows in the sub-coils 160C and 160D by the capacitor 200, which causes the main coils 160A and 160B and the sub-coils 160C and 160D of the stator 100 to generate rotating magnetic fields.
The rotating magnetic fields generated by the main coils 160A and 160B and the sub-coils 160C and 160D are transmitted to the permanent magnetic rotator 120, which leads the permanent magnetic rotator 120 to be rotated. Namely, the induction motor according to the conventional art is driven by generating driving torque through the capacitor 200 and the sub-coils 160C and 160D.
However, the induction motor in accordance with the conventional art has a problem: since the power (AC) is applied to the sub-coils 160C and 160D and the main coils 160A and 160B, magnetomotive force is lowered when the induction motor is driven initially, and since the magnetomotive force is lowered, the induction motor cannot be swiftly driven at the initial stage. That is, the induction motor according to the conventional art is driven with high efficiency after its initial driving, but it has a problem that the induction motor cannot be swiftly driven due to the low magnetomotive force when the power is initially applied to the induction motor. For example, when the voltage is applied to the sub-coils 160C and 160D and the main coils 160A and 160B, the induction motor is driven with high efficiency after its initial driving. However, when the induction motor is initially driven, since a current less than required current for the driving is applied to the sub-coils 160C and 160D and the main coils 160A and 160D, the magnetomotive force is reduced. Thus the induction motor cannot be swiftly driven at the initial stage because the magnetomotive force is decreased.
Meanwhile, the induction motor in accordance with the conventional invention is also disclosed in U.S. Pat. Nos. 6,700,270 and 6,445,092.